The effect of maternally administered diethylstibestrol (DES) in pregnancy from about the 28th day (onset of sexual differentiation) to term on the urogenital system of the offspring will be studied with special reference to the male. Based on former prenatal and perinatal studies, the offspring will be allowed to grow to puberty and will be examined for (1) anatomical changes, (b) changes in sexual behavior, (c) fertility, (d) ability to sire normal offspring. In addition, the placenta transfer of DES at different stages of pregnancy will be studied using tracers. The binding of DES to the fetal fluids and to the fetal urogenital structures will also be studied. Collateral studies using estradiol, previously shown to have little or no biological effect on the newborn genital tract of male or female, will be carried out and the reasons for the failure of the natural estrogen to affect the fetuses will be investigated. Placental transfer and binding studies will be carried out with radioactive estradiol for comparison with those using radioactive DES.